This research project deals with the analysis of fundamental principals that govern pre- and postnatal development of the primate brain. The selected structures of the developing rhesus monkey brain are studied by a combination of several advanced neurobiological methods as well as by manipulation of brain development using recently perfected methods of fetal neurosurgery. Analysis of each structure or system proceeds in the three phases. In the first phase attention is given to the interactions of brain cells as they multiply and migrate and as postmigratory neurons develop processes and establish synaptic connections that ultimately constitute the "wiring" arrangements of the mature brain. In the second phase, the consequences of selective destruction of various brain centers and/or pathways performed on the fetus which is allowed to survive are evaluated at postnatal ages in order to determine the extent of neuroplasticity and the interdependence of various brain structures. Finally, in order to relate experimental results obtained from studies in monkeys to humans, cytologically defined developmental stages correlated in both species. Projects currently under study concern: (1) immunocytochemical localization of protein 1 in the fetal monkey brain, (2) quantitative EM analysis of synaptogenetic gradients in the molecular layer of the hippocampal formation, (3) the development and regeneration in the monkey spinal cord, (4) the time of neuron origin in the various cytoarchitectonic fields of the prefrontal cortex and (5) pattern of pyramidial decussation in monkeys with normal and experimentally altered motor cortex.